bio  website  

location  Stockholm, Sweden  
age  29  
visits  member for  4 years, 11 months 
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stats  profile views  8,059 
I am interested in the moduli space of curves and also other things. I am currently on parental leave.
20h

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Map between stacks and automorphism groups
Your question has already been answer but let me give a really lowbrow comment. It's sometimes useful to think of a point with isotropy group of order $\vert G \vert$ as "$1/\vert G \vert$th of a point". So for instance if you have point of $M_g$ corresponding to a curve with no automorphisms, and it maps to its jacobian in $A_g$ which has the inversion automorphism, then this corresponds to "a whole point" mapping to "half of a point". This makes the map 2to1 in the sense of stacks. 
1d

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A functorial isomorphism in derived category
I don't think $j$ necessary takes values in $K^+(\mathcal B)$. Look at stacks.math.columbia.edu/tag/0140 
2d

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A functorial isomorphism in derived category
Why do you think my answer (to the other question) is not functorial? The truncations $\tau_{\geq n}$ are certainly functorial, and a zigzag of quasiisomorphisms in $\mathrm{Ch}(\mathcal A)$ defines functorially a morphism in $D(\mathcal A)$. And as Mariano remarks, injective resolutions can be made functorial under mild hypotheses on $\mathcal A$ (certainly satisfied for sheaves on spaces). 
Oct 16 
awarded  Nice Answer 
Oct 14 
comment 
Two basic questions on derived categories
I agree that both constructions should be functorial. 
Oct 13 
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Name for series $\sum f_n x^n / (n! (n+k)!)$
I guess the case $k>0$ arises naturally as the $k$th derivative of a doubly exponential generating function. This would seem to reduce the study of "Bessel" generating series to that of doubly exponential ones. 
Oct 13 
revised 
Two basic questions on derived categories
deleted 1 character in body 
Oct 13 
answered  Two basic questions on derived categories 
Oct 10 
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When is the Hodge diamond concentrated in $H^{n,n}$'s?
One example where the even cohomology is spanned by algebraic cycles and the odd cohomology is nonzero is the moduli space $\overline M_{1,n}$ of $n$pointed stable curves of genus one, which has odd cohomology for $n\geq 11$. 
Oct 9 
comment 
When is the Hodge diamond concentrated in $H^{n,n}$'s?
See the question mathoverflow.net/questions/151341 
Oct 8 
revised 
Why Weil group and not Absolute Galois group?
deleted 5 characters in body 
Oct 1 
comment 
$H^4(BG,\mathbb Z)$ torsion free for $G$ a connected Lie group
Don't you need $G$ to be simply connected to apply the Hurewicz theorem? 
Oct 1 
answered  Standard homology result on double complexes 
Oct 1 
comment 
(Very) High dimensional manifolds
Actually it seems the authors only prove that their example has minimal rank, not minimal dimension. Still a very nice answer. 
Sep 30 
awarded  Explainer 
Sep 29 
revised 
Connected components of the complement of a degreed affine hypersurface
added 2 characters in body 
Sep 29 
reviewed  Approve suggested edit on Connected components of the complement of a degreed affine hypersurface 
Sep 29 
answered  Connected components of the complement of a degreed affine hypersurface 
Sep 28 
revised 
Holomorphic cusp forms and cohomology of GL(2,Z)
added 893 characters in body 
Sep 28 
accepted  Holomorphic cusp forms and cohomology of GL(2,Z) 